From experimental exploration to mechanistic insight: Separation mechanism of ionic liquids for methanol-acetonitrile azeotrope

The efficient separation of methanol-acetonitrile azeotrope is critical in biofuel purification and petrochemical industries. This study utilized COSMOthermX software to calculate the selectivity of 168 ionic liquids for the separation of methanol and acetonitrile azeotrope. Subsequently, [EMIM][OAc] and [N_2,2,2,2][OAc] were identified as the most suitable ILs for the purification of methanol and acetonitrile azeotrope through extractive distillation. The vapor-liquid equilibrium data of methanol + acetonitrile + [EMIM][OAc]/[N_2,2,2,2][OAc] were measured at 101.3 kPa. With the addition of ILs, the relative volatility of acetonitrile to methanol can be improved. ILs can effectively eliminate azeotropic phenomena at specific concentrations, with a separation ability of [N_2,2,2,2][OAc] > [EMIM][OAc]. The NRTL model was experimentally fitted and found to have good fitting performance. Then, σ-profiles, excess enthalpies, and RDFs were employed to investigate the mechanism of azeotropic separation by ILs. The results revealed that the ILs interact more readily with methanol, facilitating the extraction of acetonitrile. The extraction performance of [N_2,2,2,2][OAc] was superior to [EMIM][OAc], consistent with the experimental conclusions.